Device for preparing hot water by recovering heat from waste water

ABSTRACT

A device for preparing hot water by recovering heat from waste water includes a heat pump which has a compressor and an evaporator. The evaporator supplies thermal energy to a hot water reservoir which is disposed above the compressor. At least one heat pipe thermally connects the hot water reservoir to the compressor of the heat pump and is constructed to dissipate waste heat produced during operation of the compressor to the hot water reservoir.

The invention relates to a device for preparing hot water by recovering heat from waste water by means of a heat pump comprising a compressor and an evaporator, in particular by means of a small heat pump for household applications, having a hot water reservoir, which is supplied with thermal energy by the evaporator of the heat pump.

Heat is generally recovered from waste water in devices known from practical use by means of a saturated steam circulation process. The compressor used here heats up during operation generally to temperatures in a range between around 70° C. and 90° C., which are therefore generally much higher than the temperature of the hot water reservoir which is maximum around 60 degrees. This higher temperature means that the compressor emits appreciable heat to the environment, easily amounting to more than 50 watts. This compressor heat is therefore lost so the small heat pump does not achieve a sufficiently high level of efficiency for economical operation.

A solution is already known from EP 0 114 583 A2, in which the compressor is connected directly to the hot water container. This means that during operation of the compressor heat from the compressor is emitted to the hot water reservoir but during the generally quite long idle time of the compressor heat flows in the reverse direction from the hot water container into the now colder compressor, with the result that useful heat is lost to a significant degree. To prevent this, in a device according to U.S. Pat. No. 4,448,347 the compressor is even present within the hot water reservoir, which allows better waste heat utilization but means that the structure is much more complex and therefore more expensive. It also makes the surface of the hot water reservoir larger, thereby increasing the loss of heat to the environment.

Based on this the object of the invention is to utilize the waste heat from the compressor in a simple and economical manner, in order in this way to achieve a more efficient mode of operation during the recovery of heat from waste water.

According to the invention this object is achieved in that the hot water reservoir is thermally connected to the compressor of the heat pump by way of at least one heat pipe, the hot water reservoir being disposed above the compressor and the at least one heat pipe serving to dissipate waste heat produced during operation of the compressor to the hot water reservoir.

The resulting advantages essentially consist in that, in addition to the quantity of heat transmitted by means of the evaporator, the waste heat produced at the compressor of the heat pump during its operation can also be transmitted, it being possible, as known, for said heat pipes or heat tubes to transport large quantities of heat when arranged and embodied in an appropriate manner, in so far as the heat source, in this instance the compressor, is located at the lower end of the heat pipe and the heat sink, in this instance the hot water reservoir, is located at the higher end. Such heat pipes are generally filled with a readily evaporated fluid, which collects in the region of the lower end. When this region is heated, the fluid evaporates and the vapor is distributed throughout the pipe, the vapor condensing in the colder upper region and the condensate running back down due to the gradient. Large heat flows are transported by evaporation and condensation, without requiring an external drive system.

However when the upper end is heated, heat can only be transported due to heat conduction in the thin pipe wall. As the fluid is at the bottom, evaporation does not take place and therefore neither does condensation. The heat flow is therefore much smaller from the upper to the lower end so that when the compressor is deactivated, the heat remains in the hot water reservoir.

In order to achieve the maximum possible efficiency, the invention further proposes that the heat pipe should be connected with good thermal contact to the hot water reservoir or compressor by bonding, welding or soldering by means of a connection that cannot be released on one or both sides.

It is however also possible within the context of the invention for the heat pipe to be connected with good thermal contact by means of a connection that can be released on one or both sides by way of clamping pieces or comparable connecting means connected in a fixed manner to the hot water reservoir or compressor. This solution allows more flexible construction options for the device. In particular it is easier to take apart for maintenance purposes.

It is also of advantage if the heat pipes consist of at least partly elastically configured tubes. Firstly this allows a large free selection of positions for the hot water reservoir and compressor, the only condition being that the compressor is disposed lower than the hot water reservoir. The elastic configuration of the tubes of the heat pipes means that the compressor vibrations occurring during operation can be absorbed more readily so they are not transmitted to the reservoir. This generally allows the device to operate more quietly.

In order also to avoid heat losses to the environment, it is recommended that the compressor, the heat pipes and the hot water reservoir are enclosed by a shared insulation.

It is particularly advantageous here for the insulation to be provided with a coating that reflects infrared radiation, so that no radiant heat can be lost through the insulation.

Aluminum is particularly suitable for the coating material.

In order also to keep the emission of heat produced in the compressor low, it is further recommended that the compressor has a metallic gloss, low-radiation surface. This surface is expediently made of corrosion-resistant material such as aluminum or chrome.

The invention is described in more detail below based on an exemplary embodiment illustrated in the drawing. The single FIGURE shows a schematic illustration of a device according to the invention.

The device shown only schematically in the drawing serves to prepare hot water, with heat being recovered from the waste water that results preferably with household applications by means of a heat pump. This heat pump consists in the usual manner of a compressor 1 and an evaporator (not shown in detail) as well as of a condenser and throttle valve (also not shown in the drawing). Such devices configured in the form of a small heat pump can be used in particular for household applications.

Provision is also made for a hot water reservoir 2, which is supplied with thermal energy by the evaporator of the heat pump. The hot water reservoir 2 is set up with connectors 3 (only outlined in the drawing) for water on the one hand and the cooling circuit on the other hand, the connectors 3 not being shown in detail in the drawing for the sake of clarity.

The hot water reservoir 2 is thermally connected to the compressor 1 of the heat pump by way of two so-called heat pipes 4, the arrangement being selected so that the hot water reservoir 2 is disposed above the compressor 1. These heat pipes 4 or heat tubes are filled with a readily evaporated fluid, which collects in the lower region. When this lower region is heated, in this instance by the compressor 1, the fluid evaporates and the vapor is distributed throughout the pipe, said vapor condensing back in the colder upper region and emitting the condensation heat there.

This type of heat transmission ensures that heat is transported essentially from bottom to top, as there is no fluid that could evaporate in the upper region. Heat is therefore only transported from top to bottom by way of heat conduction through the heat tube. However this component is comparatively very small. This means that the compressor 1, which is generally at a higher temperature than the hot water reservoir 2 during operation, emits heat to the hot water reservoir 2. If the compressor 1 is deactivated however, the essentially unidirectional heat transmission through the heat pipes 4 prevents heat flowing from the hot water container to the then cooler compressor 1.

To achieve optimum heat transmission, the two heat pipes 4 are in good thermal contact with the hot water reservoir 2 or compressor 1, this thermal contact consisting of either a non-releasable connection by bonding, welding or soldering or a releasable connection, with clamping pieces 5 or comparable connecting means connected in a fixed manner to the hot water reservoir 2 or compressor 1 then being provided, which accommodate the ends of the heat pipes 4.

The heat pipes 4 can consist, in a manner not shown in detail in the drawing, of at least partly elastically configured tubes, these allowing simpler assembly and a largely free selection of the position of the hot water reservoir 2 in relation to the compressor 1. The elastic tubes can also absorb the vibrations of the compressor 1 occurring during operation, so they are not transmitted to the reservoir, thereby allowing quieter operation generally.

To prevent heat loss, the compressor 1, the heat pipes 4 and the hot water reservoir 2 are generally provided with insulation in a manner that is also not illustrated in detail, it being possible for said insulation to be configured so that the compressor 1, the heat pipes 4 and the hot water reservoir 2 are all enclosed by it. In order also to shield the radiant heat within the insulation, said insulation can be provided with a coating that reflects infrared radiation. Aluminum is particularly suitable for this coating. In order also to keep any emission of infrared radiation from the compressor 1 as low as possible, it should not be painted black in the usual manner but should have a metallic gloss, low-radiation surface. A corrosion-resistant material such as aluminum or chrome is particularly recommended for this. 

1-10. (canceled)
 11. A device for preparing hot water by recovering heat from waste water, said device comprising: a heat pump comprising a compressor and an evaporator; a hot water reservoir supplied with thermal energy by the evaporator of the heat pump above the compressor; and a heat pipe thermally connecting the hot water reservoir to the compressor of the heat pump to dissipate waste heat produced during operation of the compressor to the hot water reservoir.
 12. The device of claim 11, wherein the heat pump is constructed for household application.
 13. The device of claim 11, wherein the heat pipe is permanently connected with thermal contact to one of the hot water reservoir and compressor by bonding, welding or soldering.
 14. The device of claim 11, further comprising a clamping piece fixed to a member selected from the group consisting of the hot water reservoir or compressor, said heat pipe being detachably connected with thermal contact to the member via the clamping piece.
 15. The device of claim 11, wherein the heat pipe comprises a tube having an elastic region.
 16. The device of claim 11, wherein each of the compressor, the heat pipe and the hot water reservoir comprise thermal insulation.
 17. The device of claim 11, further comprising a shared insulation enclosing the compressor, the heat pipe, and the hot water reservoir.
 18. The device of claim 16, wherein the insulation comprises a coating that reflects infrared radiation.
 19. The device of claim 18, wherein the coating comprises aluminum.
 20. The device of claim 17, wherein the shared insulation comprises a coating that reflects infrared radiation.
 21. The device of claim 20, wherein the coating comprises aluminum.
 22. The device of claim 11, wherein the compressor comprises a metallic gloss, low-radiation surface.
 23. The device of claim 22, wherein the surface comprises a corrosion-resistant material.
 24. The device of claim 22, wherein the corrosion-resistant material comprises aluminum or chrome. 